circe-lagmon-server-check: Handle circe-lagmon-server-lag being nil

That variable can be nil on an initial connection to the server,
which can result in lagmon raising an error. Handling it being
nil being basically the same as zero solves the problem.
lui-toggle-fool-display: force redisplay such that invisibility is updated

This seems to fix issue 31.
circe-network-options: Newer bitlbee users are called "bitlbee"

This used to be "root", but that changed for newer bitlbee servers.
circe-channel-message-handler: Set correct variable for RPL_ISUPPORT

This used to set a variable with a wrong name. Oops.